Mesa (master): i965/vec4: Generate better code for ir_triop_csel.

[Kenneth Graunke]

Module: Mesa
Branch: master
Commit: 6dc6e6e0d979aa666e2934ae40477195e4d37ceb
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=6dc6e6e0d979aa666e2934ae40477195e4d37ceb

Author: Kenneth Graunke <kenneth at whitecape.org>
Date:   Wed Oct 15 18:57:07 2014 -0700

i965/vec4: Generate better code for ir_triop_csel.

Previously, we generated an extra CMP instruction:

   cmp.ge.f0(8)    g6<1>D          g1<0,4,1>F      0F
   cmp.nz.f0(8)    null            g6<4,4,1>D      0D
   (+f0) sel(8)    g5<1>F          g1.4<0,4,1>F    g2<0,4,1>F

The first operand is always a boolean, and we want to predicate the SEL
on that.  Rather than producing a boolean value and comparing it against
zero, we can just produce a condition code in the flag register.

Now we generate:

   cmp.ge.f0(8)    null            g1<0,4,1>F      0F
   (+f0) sel(8)    g5<1>F          g1.4<0,4,1>F    g2<0,4,1>F

No difference in shader-db.

v2: Remember to delete the old code (thanks Matt).

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
Reviewed-by: Matt Turner <mattst88 at gmail.com>

---

 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index d0587cd..b46879b 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -1277,6 +1277,20 @@ vec4_visitor::visit(ir_expression *ir)
    dst_reg result_dst(this, ir->type);
    src_reg result_src(result_dst);
 
+   if (ir->operation == ir_triop_csel) {
+      ir->operands[1]->accept(this);
+      op[1] = this->result;
+      ir->operands[2]->accept(this);
+      op[2] = this->result;
+
+      enum brw_predicate predicate;
+      emit_bool_to_cond_code(ir->operands[0], &predicate);
+      inst = emit(BRW_OPCODE_SEL, result_dst, op[1], op[2]);
+      inst->predicate = predicate;
+      this->result = result_src;
+      return;
+   }
+
    for (operand = 0; operand < ir->get_num_operands(); operand++) {
       this->result.file = BAD_FILE;
       ir->operands[operand]->accept(this);
@@ -1780,9 +1794,7 @@ vec4_visitor::visit(ir_expression *ir)
       break;
 
    case ir_triop_csel:
-      emit(CMP(dst_null_d(), op[0], src_reg(0), BRW_CONDITIONAL_NZ));
-      inst = emit(BRW_OPCODE_SEL, result_dst, op[1], op[2]);
-      inst->predicate = BRW_PREDICATE_NORMAL;
+      unreachable("already handled above");
       break;
 
    case ir_triop_bfi: